This invention relates to vehicle electrical generators and more particularly to an alternator including a voltage regulator that, without a separate control wire from the ignition, becomes fully operational after the engine is started.
Conventional vehicle electrical generators include a voltage regulator that controls the output voltage of the generator to a calibrated voltage setpoint. When the engine is not running, the regulator goes into a low power, sleep mode of reduced current consumption, thereby preventing battery discharge. A conventional method of controlling the sleep mode is by utilizing the ignition on/off switch, indicating a desire to initiate or terminate voltage regulation.
Another method of controlling the sleep mode is a vehicle start feature that eliminates the need for a separate control wire from the vehicle""s ignition to control sleep mode. This feature wakes up the regulator only when the engine is started which it detects by means of alternator rotation. When the engine is started, it causes the generator rotor to rotate by means of a belt/pulley system. The rotating generator creates a voltage due to residual magnetism in the rotor. The detected voltage creates a signal to wake up the voltage regulator which transitions the microcontroller from a low power mode to a full operational mode.
However this method of controlling the regulator sleep mode is susceptible to DC voltage offsets, due to rectifier bridge leakage, and high frequency noise such as RF energy, that may inadvertently trigger the wake up signal. Also, the residual magnetism of a single phase is a sinusoidal waveform with amplitudes typically less than 0.2 volts peak-to-peak. The low amplitude makes it difficult to determine if actual wake up should occur, especially considering all the electrical noise present in current automotive applications. As such, this feature is used only as a backup feature triggering at higher generator rotation speeds to wake up the voltage regulator if the input from the ignition is not working properly. It is contemplated that the automatic start feature could be expanded to include the analysis of two of the three generator phases and comparing the difference between the two to determine a trigger threshold. Then two sinusoidal waveforms are 120 degrees out of phase, and generate a voltage that is 70% higher in amplitude. Although more dependable, this is not a cost-effective design.
The present invention provides a system to transition or wake up, a voltage regulator in an automotive electrical generator from a low power, sleep mode to a full voltage regulation mode in response to starting the engine without requiring input from the vehicle ignition. Wake-up occurs when the voltage regulator detects and confirms a valid frequency of rotation of the generator.
More specifically, the invention provides a control circuit configuration comprising a first filter means for eliminating high frequency noise in the voltage signal created in response to generator rotation providing a filtered signal; an amplifier means for modifying the amplitude of the filtered signal; a second filter means for eliminating the susceptibility of the signal to DC offset voltages; a detection circuit means for establishing a triggering threshold from the signal and defining an input waveform; and a microcontroller means for assessing the input waveform and controlling voltage regulator transition from low power mode to full voltage mode.
The microcontroller performs the control steps of:
initialization in response to a valid input signal;
checking the phase frequency input to determine if a valid input frequency is detected;
energizing the field coil in a fixed duty cycle if a valid frequency is detected;
changing the phase voltage gain circuit to a gain reduction that is lower than the wake-up gain;
waiting for the field coil and phase coils to energize a field strobe condition and checking the phase frequency again for a valid frequency;
transitioning to full voltage regulation upon verification of a valid frequency; and
transitioning to a low power mode upon determination that the frequency is invalid.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.